1. Field of the Invention
The invention concerns a method for supporting, at least with one supporting structure, an object made by means of stereolithography or another rapid prototype production method.
2. Discussion of the Prior Art
Stereolithography is a method known as such whereby a photopolymer is cured by means of electromagnetic rays, for example one or several laser beams which are computer-controlled. Due to the beams, the liquid photopolymer cures at the surface according to a specific pattern. The polymerized coat is usually anchored with the help of a supporting structure to a platform which, each time another coat is polymerized, sinks somewhat deeper in the liquid polymer. The supporting structure keeps the object in place during the production process and prevents deformations. Thus, the supporting structure and the object are built layer by layer. This form of stereolithography is described among others in U.S. Pat. No. 4.575.330 and EP-A-348.061.
The patterns with which pieces or objects are hardened by stereolithography or photopolymerized, have been subject to a lot of development. In different documents, optimizing of speed, of ligthening of structure and avoiding internal tensions are described for example in WO-A-89/10255, WO-A-92/20505 and EP-A-0590957. As to the support construction, the optimalization in light of the functional requirements is still very limited.
In the known stereolithography, this supporting structure is built in the shape of solid, standing walls which are usually connected to one another according to a pattern, such as described in EP-A-0338751. Especially with large objects, the building of this supporting structure requires much time, energy and material, so that this supporting structure makes the method relatively expensive. Indeed, the supporting structure is lost material. Moreover, when the object is finished, liquid material remains sticking against and in between these walls, which makes the loss of material even greater. Finally, it is often difficult to remove these solid walls from the object without damaging it or without leaving clear marks on the object.
Especially to avoid these last-mentioned disadvantages, it is already known to provide the walls with notches at the top and/or at the bottom. The notches at the top restrict the contact with the object and make it easier to remove the supporting structure. The notches also make sure that liquid polymer which is stuck between the walls under the object can flow away. However, they offer no solution for the large consumption of material of the supporting structure and the loss of liquid polymer which remains sticking against the walls, nor do they offer any gain of time.
Similar problems arise with supporting structures used for other rapid prototype production methods, generally called "rapid prototyping". Such other production methods or material growth techniques are for example other photopolymerization techniques which make use of a mask, a film, a coated glass plate or LCD plate; selective laser sintering; what is called fused deposition modelling; ink jet techniques and foil-based techniques.
With selective laser sintering of metal or plastic powders, the powder which is present in a support, which is removed afterwards, is sintered or welded with a laser or another focused heat source.
Fused deposition modelling and related techniques make use of a temporary transition from a solid material to a liquid state, usually due to heating. The material is driven through a nozzle in a controlled way and deposited in the required place as described among others in U.S. Pat. No. 5.141.680.
Foil-based techniques fix coats to one another by means of gluing or photopolymerization or other techniques and cut the object from these coats or polymerize the object. Such a technique is described in U.S. Pat. No. 5.192.559.